The present invention relates generally to bulk material handling and more particularly to a continuous feeder system responsive to the output placed upon a conveyor means, or output fed to a processing device, from a feeder control gate.
In the prior art, there have been several attempts made at controlling the flow of bulk material onto a belt conveyor or the like. For example, U.S. Pat. No. 2,792,923 to Fraubose et al discloses a system wherein the failure of the supply of material to any one or more of the different conveyors, or a reduction in the supply of material below the prescribed amount, automatically stops the drive of the motor or motors which are still conveying material. After the supply is restored, the conveyor motor or motors are again set into action automatically.
U.S. Pat. No. 2,997,205 to Schuerger et al discloses a system wherein the discharge of material from a bin or the like is controlled to hold the level of material in the bin within a predetermined range.
U.S. Pat. No. 3,042,261 to Lovette discloses a hopper gate assembly for mixing aggregate material wherein the gates may be fully or partially opened to any of several openings. The series of gates are opened and closed manually in a predetermined time sequence and in cooperation with a conveyor belt for receiving the output. If one bin runs low on its supply, the gates are closed sequentially by remote control to maintain the desired mix. Upon start-up, the gates are sequenced again, and to some degree proportionally, to assure the proper mix.
While the devices disclosed in these various patents do have advantages over a purely manual system, there are drawbacks. For example, the aforementioned systems do not provide valve control means to proportionally compensate for a change in the discharge flow rate. The output of the prior art systems are generally proportional to the weight of material in the hopper, as in the Fraubose et al '923 and Schuerger et al '205 patents, or require operator control to regulate the gates as in the Lovette '261 patent. As the weight of material in the hopper varies over time, the output varies, and the prior art systems have no way to compensate. Consequently, the accurate discharge of a selected quantity of material over a period of time is not possible.
The prior art systems also do not teach efficient control means to prevent excessive oscillation, overresponse and flow instability, which can be caused by such common material conditions as individual component size change, moisture content and lumping. Further, it has been found desirable to regulate the speed of opening and closing movement of the feeder gate to provide controlled sensitivity to changes in the flow, which is clearly not contemplated in the prior art.
Furthermore, the prior systems do not lend themselves to accurately control the discharge flow rate within a relatively small range. This function may be of considerable importance with respect to accurately formulating a final product made from a mixture of different bulk material streams. As one example, it is important to exactly maintain the proper proportions when mixing coals of different origins for coking in a coke oven.
Other systems for flow control use vibratory and reciprocating bed feeders. For high material flow requirements, these feeders become very large and massive, and are expensive to buy and maintain. These systems depend on vibrating masses to control the material flow and as the mass flow goes up, so does the size of the feeder components required to transmit the forces. Also, these feeders are basically volumetric control devices and are difficult to control for mass flow.
Futher, as inevitable parameter variations occur, such as component size change, moisture content and lumping, the problem of erratic flow of material in this type of system is greatly increased. This is so since the actual feeding action from the vibrating bed must be transmitted through layers of the product and as changes occur in the parameters the feed inevitably changes. As the vibrating action is changed in an attempt to compensate, the deleterious "hunting" of the systems occurs.
For large mass flow applications, the energy consumption of vibrating systems is relatively high, providing another disadvantage to this type of prior art system.
Thus a need and broad objective is identified for a new approach to controlling mass flow of bulk material wherein the problems inherent in the prior art systems are avoided. In particular, a feed control system that attains the objectives of being highly responsive and yet stable, inexpensive to build and operate and energy efficient is identified. With this as background, the basis for the following additional objects is formed.